The cerebral cortex is a complex network of neurochemically-defined subpopulations of cells. Understanding how distinct neural populations interact to generate the dynamic electrophysiological oscillations that characterize the cerebral cortical network during wake and sleep is a pressing challenge to the field of neuroscience. There is a critical unmet need for novel experimental resources to address hypotheses in this context. We have developed a novel transgenic mouse line (NPY-ChR2- eYFP) in which the neuropeptide Y (NPY) promoter drives expression of the light-sensitive cation channel Channelrhodopsin2 (ChR2) and the marker protein enhanced yellow fluorescent protein (eYFP). A subpopulation of Npy-positive cells in the cerebral cortex (sleep-active neurons; SANs) is a putative regulator of sleep-dependent changes in cerebral cortex network slow wave activity, plasticity and blood flow. Our preliminary data demonstrate that the transgene is expressed in the brain, and that optogenetic manipulation of the cerebral cortex triggers an increase in slow activity in the electroencephalogram of transgene-expressing mice. These data demonstrate that an optogenetic strategy to manipulate cerebral cortical neuronal network properties in these animals is feasible. The overarching goal of this work is to develop a set of protocols in which NPY-ChR2-eYFP mice can be used to delineate the functions of the cerebral cortical NPY-expressing interneuron population generally, and the SAN population specifically, in generating cerebral cortical electrophysiological events. We will achieve this goal by pursuing two aims. In Aim 1, we will use immunohistochemistry to verify that the NPY-ChR2-eYFP construct targets transgene expression to NPY-positive cells and SANs in the cerebral cortex. In Aim 2, we will optimize optogenetic stimulation protocols for manipulating the activity of the target cell population in vivo. Collectively, these studies will yield a set of protocols to advance our knowledge of the function of the NPY-positive population in regulating cortical electrophysiological oscillations. Additionally, the transgenic mouse line and protocols for experimentation on this line will become a public resource applicable in other areas of research such as neurovascular coupling, neural regulation of stress responses and feeding, and the pathophysiology of stroke.